Find this angle given the triangle's Orthocenter

In summary: And another clue to solve the problem: After you showed that the first portion A is equal to the third portion A, then by this and by knowing that AH=AO=R and AD=2R , try to prove 2AE=AB (by similarity)
  • #1
kaloyan
4
0
Homework Statement
An acute ##\triangle ABC##, inscribed in a circle ##k## with radii ##R##, is given. Point ##H## is the orthocenter of ##\triangle ABC## and ##AH=R##. Find ##\angle BAC##. (Answer: ##60^\circ##)
Relevant Equations
-
243002

##AD## is diameter, thus ##\angle ACD = \angle ABD = 90^\circ##. Also ##HBDC## is a parallelogram because ##HC||BD, HB||CD##. It seems useless and I don't know how to continue. Thank you in advance!
 
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  • #2
What drawing program did you use to make that figure?
 
  • #3
LCKurtz said:
What drawing program did you use to make that figure?
I've used GeoGebra.
 
  • #4
This actually doesn't have one answer. just put A=70 for example, and it won't go wrong, or 60, and etc.
 
  • #5
ali PMPAINT said:
This actually doesn't have one answer. just put A=70 for example, and it won't go wrong, or 60, and etc.
I don't get what you are trying to say. If you try to draw the same picture with an angle of ##70^\circ## you don't get the lengths ##AH = AO##.
 
  • #6
LCKurtz said:
I don't get what you are trying to say. If you try to draw the same picture with an angle of ##70^\circ## you don't get the lengths ##AH = AO##.
Oh, yes, you are right. For reasons, I thought any angle would be correct
 
  • #7
kaloyan said:
Problem Statement: An acute ##\triangle ABC##, inscribed in a circle ##k## with radii ##R##, is given. Point ##H## is the orthocenter of ##\triangle ABC## and ##AH=R##. Find ##\angle BAC##. (Answer: ##60^\circ##)
Relevant Equations: -

View attachment 243002
##AD## is diameter, thus ##\angle ACD = \angle ABD = 90^\circ##. Also ##HBDC## is a parallelogram because ##HC||BD, HB||CD##. It seems useless and I don't know how to continue. Thank you in advance!
So, you can continue by showing first portion A is equal to the third portion A, Then try to use trigonometry since AH=AO=R and AD=2R, and then you will get the answer.
 
  • #8
ali PMPAINT said:
So, you can continue by showing first portion A is equal to the third portion A, Then try to use trigonometry since AH=AO=R and AD=2R, and then you will get the answer.
I'm 8th grade - I do not know Trigonometry.
 
  • #9
kaloyan said:
I'm 8th grade - I do not know Trigonometry.
What about similarity? It can be solved by it.(I don't know how is your country's education system)
And another clue to solve the problem: After you showed that the first portion A is equal to the third portion A, then by this and by knowing that AH=AO=R and AD=2R , try to prove 2AE=AB (by similarity)
 

What is the orthocenter of a triangle?

The orthocenter of a triangle is the point where all three of the triangle's altitudes intersect. An altitude is a line that passes through a vertex of the triangle and is perpendicular to the opposite side.

How do you find the orthocenter of a triangle?

The orthocenter of a triangle can be found by constructing the altitudes of the triangle and finding their point of intersection. Alternatively, it can also be found by using the formula: Orthocenter = (a^2h_a + b^2h_b + c^2h_c)/(a^2 + b^2 + c^2), where a, b, and c are the side lengths of the triangle and h_a, h_b, and h_c are the altitudes.

What is the relationship between the orthocenter and the centroid of a triangle?

The centroid of a triangle is the point where all three of the triangle's medians intersect. A median is a line that passes through a vertex of the triangle and the midpoint of the opposite side. The orthocenter and centroid of a triangle are always collinear, meaning they lie on the same line. The centroid divides the line segment between the orthocenter and the vertex in a ratio of 2:1.

How many orthocenters can a triangle have?

A triangle can have only one orthocenter. This is because the three altitudes of a triangle are always concurrent, meaning they intersect at one point. Therefore, the orthocenter is a unique point for every triangle.

What is the significance of the orthocenter in triangle geometry?

The orthocenter is an important point in triangle geometry because it is related to other important points such as the centroid, circumcenter, and incenter. It is also used in various theorems and constructions, such as the construction of the Euler line and the proof of the orthocenter theorem. Additionally, the orthocenter helps to define the orthic triangle, which is formed by the feet of the altitudes of a triangle.

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